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Guide to distinguishing mold contamination from other building stains, debris, or particles.
This article describes indoor stains and deposits that are not building mold or in other examples, harmless cosmetic mold. When investigating a building for a mold problem, you can save mold test costs by learning how to recognize Stuff that is Not Mold or is only Harmless Mold but may be mistaken for more serious contamination - save your money.
Because people sometimes send "mold test" samples to our lab that really should not have been collected, much less looked-at, I provide this library of photographs of things that are "not mold" and don't need to be tested.
These are substances that you can easily learn to recognize in buildings. Save your mold test money, and increase the accuracy of your mold contamination inspection or test for toxic or allergenic mold in buildings: review these items to learn recognize non-fungal materials or even possibly harmless cosmetic black mold often mistaken for toxic fungal growth.
For photos of stuff that is indeed mold contamination in buildings, see MOLD APPEARANCE - WHAT MOLD LOOKS LIKE. So many people have called us to look at things that are not mold that I'm offering some photo tips below.
Don't hire an environmental consultant if your only concern is the stuff you see here and if there are no health or air quality complaints. Save your money, don't bother testing the things you see below.
Finding "not mold" material in a building does not mean that there is no mold or allergen problem.
Even relatively harmless house dust collected on a surface and sent to a lab as a mold screening test can contain a surprising amount of problematic mold spores if the building has a mold problem.
More important for mold testing, right in among an old colony of harmless cosmetic black mold I've on often found hard-to-see Aspergillus sp. or Penicillium sp. mold that grew there much after the original black mold deposit.
Judgment and common sense are needed. Nonetheless, the examples below are unambiguous and should not be sampled for mold testing.
Photo: white deposits on floor framing over a basement of an older U.S. home were examined in our laboratory and identified as inorganic salts and minerals, possibly remains of a lime-based paint.
However water stains on some of the wood and a few chains of of Aspergillus sp. spores found in the surface samples from these joists suggested that a further check of other surfaces and materials to look for watger damage and mold growth would be justified.
[Click to enlarge any image]
Photo: construction adhesive used to bond the plywood subfloor to the floor joists can get smeared or can drool and drip down into the space below. This photo, originally posted as a reader question at MOLD CONTAMINATION IN BUILDINGS shows adhesive, not mold.
In the articles listed here we describe sometimes-scary-looking stuff on surfaces: but stuff that is not mold, does not require mold testing, but which may still help diagnose building conditions and history. We discuss, describe, and provide photographs of some common items that are sometimes mistaken for mold in buildings.
What about white fluffy "growth" or stuff on walls, particularly masonry walls? You may be looking at efflorescence - which is not mold.
What about brown or even reddish or darker bubbly stuff that seems to be "growing" on masonry or plaster walls? You may be looking at efflorescence - which is not mold.
Be sure to go to EFFLORESENCE & WHITE or BROWN DEPOSITS to review our photos and text on how to recognize mineral efflorescence that is likely to be found on concrete block, stone, brick walls, foundations, and chimneys.
This white fluffy material is efflorescence, a crystalline mineral salt left behind as moisture comes through the wall and evaporates into the building interior.
Brownish or reddish bubbly efflorescence and dirt deposits on walls may be a mix of mineral efflorescence and other salts and debris left behind as water or moisture pass through building ceilings or walls.
Efflorescence is not mold, though it is an indicator of wet conditions that could contribute to a mold problem somewhere in the building.
In sum, although efflorescence is not mold, it often indicates wet conditions that cause problem mold growth elsewhere in the same building.
You'll need to identify the sources of moisture or leaks and correct them, and depending on other building air quality complaints or health concerns it may be appropriate to inspect and screen the building for problem mold or other moisture or water-related problems.
What about those clear or opaque spherical brown blobs we see on rafters in attics? Is that toxic brown mold?
Probably not. Take a look at this photograph.
Wood sap on rafters in a hot attic forms hard shiny brown or tan spheres that some people think is mold.
This is not mold, it's sap crystals that have been extruded from the wood due to high attic temperatures.
We see more of this sap staining when the wood used for framing was not kiln dried before construction.
Some mold-suspect material in buildings is easily determined to be spray foam insulation.
Sprayed icynene foam insulation [photo] is not mold either. Though we sometimes find fungal growth in buildings that looks a lot like this substance, it would be very odd for it to appear so extensively and so uniformly as the foam insulation shown in this photo.
For more information about foam spray insulation such as Icynene foam, see ICYNENE FOAM SPRAY INSULATION and
for an older foam insulating product seeUREA FORMALDEHYDE FOAM INSULATION, UFFI
To compare actual mold growth with crawlspace foam insulation see this photograph of yellow mold growth [photo] taken from a rotting wood truss in a wet crawl space.
You'll see it looks a bit like the sprayed foam insulation shown on this page.
But actual yellow mold growth on wood won't be found in a continuous blanket such as shown in our photograph of icynene foam on this page.
See INSULATION INSPECTION & IMPROVEMENT for details about foam and other building insulation types;
see FIBERGLASS HAZARDS for a discussion of mold problems in fiberglass insulation;
see MOLD in FOAM INSULATION for a discussion of when and why we find mold growth on foam insulating materials like foam board and air handler foam insulating board.
may be found where moisture condenses on cool building surfaces. Warm moisture-laden air touches the cooler surface of a building wall or ceiling, giving up some of its moisture to the surface as condensation.
As air moves through the building, typically up walls and across ceilings, debris in the air, particularly soot such as that left by burning scented candles, adheres more to the damp surfaces than to others, leaving black marks or "tracks."
In a conventionally-framed wood structure, wall and ceiling framing is typically on 16" or 24" centers.
The wall or ceiling will be cooler where the framing is located than will be the spaces which are not touched by framing and which, perhaps, are insulated.
So if you see black streaks up the building wall in a regular 16" or 24" pattern, particularly on cooler exterior walls but potentially anywhere, it may be thermal tracking.
If you have frequent fireplace fires, cooking, or if you burn scented candles, if people smoke in your home, or if your oil-fired or gas-fired heating system is not working properly, the added soot particle load in the building air is not only a health concern (soot and potentially lead), it also will mark the building surfaces in this characteristic pattern.
See our complete article on THERMAL TRACKING BRIDGING GHOSTING
BBMS is a term we coined for the phenomenon which describes an observer who is certain that a condition s/he has recently seen is a new condition even though solid forensic evidence shows that the condition is long-standing.
BBMS occurs when a person who has (other) reasons to be anxious about health or structural or safety conditions in a building (or any other condition where BBMS may apply) observes some mark, material, or substance for the first time
In other words, the condition or clue, mark, or substance was there before, but the person had no reason to attend, recognize, and consider it.
BBMS occurs most often (in our experience) where health concerns are present and people have become worried about mold contamination, or where structural concerns are present and people have become worried about cracks, stains, or possible indications of building damage.
Basketball print mold: A client was certain that a large collection of round black speckled marks on his garage ceiling were toxic mold, that the marks were growing in size, and that they had not been there when he purchased the home a few years before.
During a mold investigation we had seen and rapidly discounted the significance of these marks, preferring to follow water leaks and moisture to an actual building problem. To an experienced eye it was immediately obvious that the marks had been made by a basketball which someone had bounced against walls and ceilings.
It is important to realize that a stain or mark may have been in place but un-noticed for a long time on a building surface.
In its form of black on white on the garage ceiling the stain pattern was a bit hard to see. We used this trick of reversing black and white in the lab computer, making the basketball characteristic surface pattern of the ceiling marks which we sampled quite obvious.
We explain why this confusion about building clues and mold risk happens in a separate page: please see BASKETBALL MOLD SYNDROME - BBMS
BLACK STAINS from ANIMALS for examples of animal stains that are sometimes mistaken for mold in buildings.
COSMETIC vs HARMFUL MOLD: Can Mold Make You Sick? Fear of Mold - Mycophobia - Can Lead to Unnecessary Expense
FOUNDATION DIAGNOSISfor examples of procedures used to diagnose and evaluate foundation wall and slab cracks and movement.
MOLD INFORMATION CENTER for guidance on what to do about mold and other indoor air quality issues
With a little thought we can easily distinguish pet stains on drywall from thermal tracking by the stain pattern and location as well as other details such as the absence of a heat source, or the identification of a location where we'd expect a pet to rest.
Similarly we can identify black stains on walls where people's heads rested while sitting on furniture or in bed (see photo link just below).
Black marks on interior walls [image] such as the black "mold suspect stains" shown on the white painted drywall in this photo might be just be where the dog [photo] lay on the floor against the wall (stain at floor level in this picture) or in this photograph of black stains higher on a wall where people rested their heads [image] in bed.
DUST, HVAC CONTAMINATION STUDY which turned out to be cotton and other carpet fibers having nothing to do with the Heating or Cooling equipment was discussed at our Fear of Mold WebLog or "Blog" where we periodically post results of interesting forensic investigations.
House dust might be a contributor to building air quality complaints IF the dust has high levels of problem particles such as mold, dust mite fecals, pollen, sub-micron particulate debris, bacterial contaminants, pet hair, mouse dander or fecal dust, and similar particles.
POLLEN_PHOTOS provides advice including a pollen photo ID library. Pollen may be allergenic, but it's not mold and requires a different approach to detection and cleaning indoor spaces.
Some black mold in buildings arrived on the framing lumber and is harmless both to humans and to the building materials on which it is found. Often a visual inspection for certain clues (discussed below) can make you very confident of when mold appeared on lumber and what sort it probably is.
We discuss how to recognize and what to do about harmless mold, harmless black mold, and cosmetic molds in our article: HARMLESS COSMETIC MOLD
Make sure that the obvious harmless "black mold" you see (such as shown in the photograph at left) is the only mold growth found.
Photo-oxidation or weathering that affects wood left exposed to the weather can leave un-painted wood surfaces a gray or even a dark brown color.
We often see this effect on framing lumber that was left uncovered in storage or at the lumber yard. We may also see reddish-brown to gray oxidized wood surfaces on all sides of rafters in poorly-vented attics that have been very hot.
Characteristic of this wood coloration pattern is that just one side of the lumber - that exposed to sunlight - will be dark in color.
The following Q&A may be an illustration of this wood stain or oxidation question, though without a lab test we couldn't be sure that there was no mold on the treated wood (sometimes a host for fungal growth) or on other wood surfaces in the attic shown here.
Do you think this is a mold problem on our roof rafter. L.P. 1/13/2013
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem. That said, here are some things to consider:
What the heck - it looks as if that roof is framed over a very very long distance with just 2x6's
I can't be sure from just your photos, but from what I see so far one wonders if the roof is under-framed and lacks proper strength (photo above left).
At above right we can see that someone banged in some additional support between existing rafters using what looks like treated lumber. The fact that the dark color is just on one face of some rafters (photo at above left) and does not extend around the corner from the flat side to the rafter edge is NOT characteristic of in-situ mold growth - more like the wood was left outdoors and weather exposed before it was put to use
The fact that the dark color also does not grow over from rafter faces onto roof sheathing is a similar argument against mold growth on these surfaces since the time of construction
To know for sure what's on the wood surfaces would require a lab test or two. I wouldn't spend the money unless there were other reasons to be concerned about this area.
See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for help figuring out if such investigation is warranted.
I checked your site and I couldn't find anything on this. This is between the joists in my basement. I removed Sheetrock and insulation and found it. Thanks - M.R. 1010/17/2013
I've been thinking about this and your photo - it's not something I've seen inside a building before; the growth pattern looks a bit like algae; but those black dots may be fungal spores or ... something else. Mold growing in the pattern of a fern leaf or bracken pattern is not one I've found before.
On the side of what looks like a floor joist in your photo is what looks a bit like fungal growth of basidiomycetes - I don't know from such limited data; IF it's fungus there you should be looking for rot and structural damage; Is that shiny property in the photo because the surfaces are wet? Where is this - geography, building type?
If you can collect suspect material on a tape sample (or if not try a razor blade and a clean plastic baggie or hard plastic container) you are welcome to send me a couple of samples and I'll take a look in the lab. For tape samples try the procedure (and address) at MOLD TEST KITS
4/7/2014, Reader Michael Sears said: these may be marks from honeybee or feral bee honeycombs
I just saw your image inspectapedia.com/mold/Algae_or_Mold_939_MR_DJFs.jpg [the photograph just above]
I believe these are marks left over from the removal of a bee hive. The fern pattern is where the honey comb connected to the subfloor.
Thanks Michael. I took a look at several resources on how people remove honey bee colonies from buildings (traps are good but there are also special vacuums that don't harm the bees), before finding one of them, the E.C. Mussen (U.C. Davis) citation below that included photos not of the marks left behind by a honeybee comb on a building surface but of some feral beehive structures that could have made marks similar to those in the photo above.
Additional information is in a nice article by Keith Delaplane at the University of Georgia, also cited below.
In Delaplane's photos we see that some of the bee honeycombs built in a building wall cavity (and presumably similarly under a floor as in our photo above) are placed on-edge in a manner (see Delaplane, Fig. 3) --that might leave the marks we are discussing.
Watch out: don't kill bees if you find them swarming in or around your home. Given recent decimations of bee populations world wide we desperately need all the bees we can get. If you don't think there is a serious bee shortage, just take a look at people in China climbing trees with Q-tips to pollinate flowers on fruit trees. Call a bee expert for help.
Thanks for the reply. I don't see any structural damage to the floor joist or sub-floor. Whatever it is, appears to be on the surface.
I'm located outside of Hudson, NY. My house was built in the 70's and we have lived here for 4 years. When I moved in the basement was finished, Hurricane Irene changed that. We got flooded, a significant portion of the foundation cracked and began to collapse. We had mold everywhere. Long story short, we scrapped everything in the basement, gutted it, rebuilt the foundation and started over.
This spot of fungus or mold, however, was not touched by the flood. Which is why I hadn't removed the drywall and insulation until now. And I was surprised to find it, because everything around it is in good shape.
The shine in the picture is probably from bleach solution I sprayed on it. However the fungus had a sheen before I sprayed it. It has a waxy appearance, but it's not soft, in fact I had a hard time trying to scrape it with a putty knife. The bleach solution and scraping have not had much affect.
I would like to test this to see what it is. How much do these tests usually cost? My primary concern is the health of my family, and second I want to remove any problems before I finish my basement.
Sharp photos would be helpful, not just closeups, but the situation in the basement and perhaps an outside photo of the house distant enough that I can see what surface drainage looks like. I'll look at your samples pro-bono - in our own forensic laboratory.
If you can't get something on a tape, best possible sample would be a wood scrap (not a wood "scraping" that had the material on its surface; second best is to try to carefully cut or slice off a sample and package it in a rigid container so it's not turned into powder before I can see its structural properties.
Knowing the history of the house, prior flooding, is helpful in evaluating the risk of hidden mold. About the prior flood and cleanup, you want to be sure that moisture from flooded lower floors didn't create a hidden hazard in upper building wall cavities or ceiling cavities.
The sample received was wood fragments ranging from about 1/2cm to ultra-fine powder. I prepared test samples by trying a tape lift from the largest fragments (best results) and additional samples from pulverized fragments and from dust in the plastic bag containing the original fragments.
Details of the actual slide preparation from the scraping sample submitted by M.R. are found at MICROSCOPE SLIDE BULK SAMPLE PREP.
These samples were mounted in lacto-phenol with a trace of cotton-blue dye and were examined microscopically at various magnifications up to 1200x.
Given that I though we were looking at a fern-like bracken mold growth pattern I suspected there may have been an artifact such as a residue left by prior plant material pressed on the subfloor. It seems I was wrong.
And I was surprised to find plenty of fungal spores in the scrapings you sent me, though unfortunately sending scrapings rather than a tape lift of the surface fails to capture the growth patterns themselves - data that would have been most helpful.
Spores varied in size, shape and color, probably due to variations in bleach treatment and hydration in my mountant; the most well defined photos (below) resemble Periconia-like fungal spores, but of a too-light color - a condition that I guess could be due to having applied bleach.
My identification is uncertain due to sample condition, but I've asked a couple of fellow microscopists for help in case anyone has seen this fern-like or bracken-like fungal growth pattern before.
I could not locate the pattern in my references and will continue to research the matter.
We welcome comments (CONTACT) from others about the identification of this fungus.
Bleaching mold, as you report you did, is pretty irrelevant. (BLEACHING MOLD, Advice about)
As we can see even in this sample, it does not "kill" every spore - some remain viable - or at least the spore colors and physical condition vary widely from fragments and hyaline spores to dark brown or bleached yellow fungal spores.
More to the point, depending on the species, some fungal spores remain allergenic or toxic even if non-viable (bleached to death) and may still contain mycotoxins. Such mold at high levels and particularly if airborne could still be a problem for some people in the building.
The proper approach to indoor mold contamination is to remove the mold, clean the surfaces, and fix the original cause for mold growth.
Given the conditions you've described I'd not be particularly worried about the remaining spores - once you've cleaned off what can be physically removed, dried, and then sealed the surface your attention needs to be on finding and fixing sources of leaks, water entry, high moisture.
I attach two spore photos for your enjoyment. If you are able to obtain a clear adhesive tape lift of the surface in the actual growth pattern we saw in your original photograph that would be most helpful.
At the top of this article we showed another photo of these white deposits on wood floor joists in an older U.S. home. This is not mold but an inorganic deposit, possibly lyme paint or a similar coating.
Similar stains or deposits can also be found on wood framing in a more gray color as cement deposit left on wood used first as concrete forms, later salvaged for use in building construction.
Other white deposits found on building surfaaces may be
There is a white, flaky, crusty substance in my basement on the floor joists around the outside perimeter in the laundry and utility room. The pattern looks like mold, but the color is wrong. I posted photos on my Google Drive for public viewing. Short URL is ... .
I've had two home inspectors through the house in three years. One for my pre-inspection before I bought the house, and one before putting the house on the market to sell. Neither one called it out.
But I'm over 90 days on the market with no offers, below market price in a good neighborhood, and wondering if this stuff may be scaring people away that are too polite to mention it. Your feedback is welcomed.
[Click to enlarge any image]
The substance on the floor framing in your photos is not mold, it is a flaking-off white spray coating, I suspect either a paint or lyme coating. Your first photo (above) shows the white spraypattern taht coated the floor joists, rim joist, wall top framing, and contined across a vertical galvanized metal pipe.
It would be instructive to make a good guess at why the spray was applied. If there were insect damage, particularly powder-post beetles or old house borers (that I did not see in your photos) a coating is sometimes used to make more apparent whether or not the insects are active.
Above we can see paint flakes peeling off of the wood surface, and some peeling paint has fallen away completely, showing the wood surface of the floor joists. You may from time to time see more of these paint flakes on the floor below: the peel and fall-off rate probably depends on the moisture conditions in the basement as well as the paint age.
See PAINT FALURE, DIAGNOSIS, CURE, PREVENTION for more about peeling paint on building surfaces.
If there was a history of basement water entry - an important concern to home buyers - someone may have sprayed paint to cover water stains or to paint-over a waterproofing sealant applied to the foundation wall below.
Having inspected thousands of homes over many decades, I have very rarely found conditions so severe that one would question the very idea of buying the home - perhaps 3 or 4 times in 8-10,000.
Every home inspection finds items in need of attention: conditions that are Dangerous, causing rapid Damage or Deterioration to the building, or that flat Don't work and are needed (Dan's "3 Ds"). A buyer needs to know about these in order to have a realistic financial plan for the home.
If a buyer likes the home, location, and price, I'd expect them to ask you or your realtor about any 3-D findings that result from the inspection, (even though their home inspector should have discussed his or her observations only with the person who hired him).
If your realtor is on the ball he will perhaps convey to potential buyers that you are open to hearing about and considering (in negotiation) legitimate findings or concerns that the buyers may have. That may make you better informed.
Be sure to see our full article: MOLD APPEARANCE - WHAT MOLD LOOKS LIKE that has photographs and descriptions of what real mold looks like inside a building.
But be careful, some of the most problematic common indoor molds, the Aspergillus sp. and Penicillium group can be very light in color and hard to see on building surfaces.
We offer tips on how to look for mold for these hard-to-see molds too: See MOLD in BUILDINGS
If you need to see what other indoor allergens look like in a building contact us (our contact information is below and at the "More Reading" links at the bottom of this article ).
Continue reading at MOLD APPEARANCE - WHAT MOLD LOOKS LIKE - or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see MOLD APPEARANCE on VARIOUS SURFACES - INDEX to return to the full list of photographs of the appearance of mold on various building materials & contents.
Or see MOLD APPEARANCE, STUFF THAT'S NOT MOLD - FAQs - questions & answers posted originally on this page
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Questions & answers about stains and growths in buildings that are not mold were posted originally on this page are now found at MOLD APPEARANCE, STUFF THAT'S NOT MOLD - FAQs.
Please also see more questions and answers about building stains that are not caused by mold growth: STAINS NOT MOLD, FAQs
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